Cell type-specific epigenetic control of brain function

Cincinnati Childrens Hosp Med Ctr, Cincinnati OH

Investigators

Abstract

Summary: There are no effective treatments for the majority of brain disorders. Even diseases like epilepsy, for which many powerful therapies exist, are intractable in about one third of affected individuals. One of the reasons that make treating brain disorders like epilepsy so difficult is the complexity of the underlying pathology that is tough to correct with single-target approaches and poorly understood. Recent preclinical studies have begun to address this challenge by exploring aberrant microRNA-induced silencing as a pathological mechanism contributing to epilepsy. MicroRNA-induced silencing is a powerful epigenetic mechanism that controls neuronal function and is dysregulated in epilepsy. MicroRNAs repress translation or initiate the degradation of hundreds of target mRNAs and can regulate several components of the same biological pathway. This makes them powerful regulators of biological processes but also imposes a substantial challenge to maintain functional specificity. MicroRNA specificity in the brain is most likely achieved through different molecular environments in specific cell types and brain circuits; yet, not much is known about these factors which prevents the field from fully understanding their biology as well as their potential and risks as drug targets. The proposed research will address this challenge by using novel adeno-associated virus (AAV)-assisted strategies to reveal the cell types and cell type-specific target mRNAs that mediate microRNAs’ control of brain function in the context of epilepsy. Based on preliminary data suggesting that effects of a specific microRNA on seizure control and neuronal morphology are mediated through different cell types, the proposed research will test the central hypothesis that microRNA specificity is achieved through cell type- and brain circuit-specific control of microRNA function, so that for select proconvulsant microRNAs, the effects on seizures and healthy brain function can be separated by cell type and mRNA targets. To test this hypothesis, a two-pronged approach will be followed to (1) assess cell type-specific control of brain function of key microRNAs critical in epilepsy, and (2) identify their cell type-specific target mRNAs to reveal the molecular pathways contributing to their diverse functions. Leveraging the synergistic expertise of a multidisciplinary team in microRNA biology, epilepsy, cognition, and gene network analysis, two aims are proposed. In aim 1, microRNAs will be inhibited either pan-neuronally, in excitatory neurons, in inhibitory neurons, or in astrocytes to identify the cell types that mediate control of seizure susceptibility and recurrent seizures in epilepsy, neuronal dendritic spine morphology, and cognition. In aim 2, cell type-specific inhibition of microRNAs combined with isolation of mRNAs silenced or actively translated only from cells in which the microRNA is inhibited, will be used to experimentally identify the cell type-specific mRNA targets of, and thus biological networks regulated by, the same microRNAs as tested in aim 1. This research will provide essential insight into fundamental function of microRNAs in the brain and will be a critical step towards fully understanding the potential of microRNAs as treatment targets in epilepsy and other brain disorders.